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J Bacteriol, April 1998, p. 1632-1641, Vol. 180, No. 7
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

The CIRCE Element and Its Putative Repressor Control Cell Cycle Expression of the Caulobacter crescentus groESL Operon

Regina Lúcia Baldini, Marcelo Avedissian, and Suely Lopes Gomes*

Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, São Paulo 05599-970, Brazil

Received 28 October 1997/Accepted 2 February 1998

The groESL operon is under complex regulation in Caulobacter crescentus. In addition to strong induction after exposure to heat shock, under physiological growth conditions, its expression is subject to cell cycle control. Transcription and translation of the groE genes occur primarily in predivisional cells, with very low levels of expression in stalked cells. The regulatory region of groESL contains both a sigma 32-like promoter and a CIRCE element. Overexpression of C. crescentus sigma 32 gives rise to higher levels of GroEL and increased levels of the groESL transcript coming from the sigma 32-like promoter. Site-directed mutagenesis in CIRCE has indicated a negative role for this cis-acting element in the expression of groESL only at normal growth temperatures, with a minor effect on heat shock induction. Furthermore, groESL-lacZ transcription fusions carrying mutations in CIRCE are no longer cell cycle regulated. Analysis of an hrcA null strain, carrying a disruption in the gene encoding the putative repressor that binds to the CIRCE element, shows constitutive synthesis of GroEL throughout the Caulobacter cell cycle. These results indicate a negative role for the hrcA gene product and the CIRCE element in the temporal control of the groESL operon.

* Corresponding author. Mailing address: Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, CP.26.077, São Paulo, SP 05599-970, Brasil. Phone: 55-11-815-3286. Fax: 55-11-818-7986. E-mail: sulgomes{at}quim.iq.usp.br.




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